Polyoxymethylene (POM, also known as polyacetal) has excellent tribological characteristics, hardness, stiffness, moderate toughness, low coefficient of friction, good solvent resistance, and the ability to crystallize rapidly, making polyoxymethylene resin compositions useful for preparing articles for use in many demanding applications. However, during melt-processing, polyoxymethylenes can degrade and release formaldehyde. For this reason, formaldehyde evolution, measured as thermally evolved formaldehyde (TEF) is often used to determine the heat stability of polyoxymethylene compositions. Other methods for assessing the heat stability of polyoxymethylene include the measurement of weight loss in air over aging at elevated temperatures for prolonged periods, such as 500 to 1000 hrs and the observation of degradative coloration of the resin compositions using the Yellowness index, as defined in ASTM E313-73 (D 1925).
In the manufacture of automobile interior parts, reducing emission of volatile organic compounds (VOC) such as formaldehyde increasingly demanded. It would be desirable to have polyoxymethylene compositions, especially used in automobile interior parts that exhibited good or excellent thermal stability during melt-processing and aging, as assessed by one or more of the above-mentioned methods.
U.S. Pat. No. 5,011,890 discloses polyacetal compositions including polymers having formaldehyde reactive nitrogen groups such as polyacrylamide. The use of epoxidized fatty acid stabilizer as polyoxymethylene stabilizers has been disclosed in U.S. Pat. App. Pub. No. 2005/0288438. U.S. Pat. No. 5,418,286 discloses a polyacetal resin with certain epoxy-containing polymer compounds. U.S. Pat. No. 5,866,671 discloses polyacetal compositions having organic cyclic compound, including hydantoin compounds, exhibiting liberation of low concentrations of formaldehyde. U.S. Pat. App. Pub. No. 2007/0078204 discloses a polyacetal resin composition and article thereof comprising a hydrazide compound having reduced emission of formaldehyde.